[TASK] Make RteHtmlParser entrypoint API cleaner

The RteHtmlParser has two public methods:
->init()
->RTE_transform()

init() was introduced in early PHP4 times when there was no constructor in PHP.
RTE_transform() contained a lot of parsing of properties, which is not needed
anymore since TYPO3 v8. init() itself is not needed anymore.

Since TYPO3 v8, RteHtmlParser is much cleaner towards the developer,
and the last step for this PHP class is to clearly separate the logic for the transformations in each direction, making two new entrypoints:
->transformTextForRichTextEditor($content, $configuration)
->transformTextForPersistence($content, $configuration)

This way, all logic is separated in these two methods, and the existing
RTE_transform() method is just a shell, which is not needed anymore.

Resolves: #90258
Releases: master
Change-Id: Iba140d71c5cd954dab4cf1fe4bfaca2233527e50
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/63070


Tested-by: TYPO3com <noreply@typo3.com>
Tested-by: Susanne Moog <look@susi.dev>
Tested-by: Daniel Goerz <daniel.goerz@posteo.de>
Tested-by: Benni Mack <benni@typo3.org>
Reviewed-by: Susanne Moog <look@susi.dev>
Reviewed-by: Oliver Hader <oliver.hader@typo3.org>
Reviewed-by: Benni Mack <benni@typo3.org>